1. Field of Invention
The present invention relates generally to the field of combustion furnaces and methods of use, and more specifically to improved submerged combustion melters and methods of use in producing molten glass.
2. Related Art
Glass melting furnaces have traditionally been of rectangular shape due to the issue of construction with refractory blocks and ability to control the flow of the molten glass through the melter. (Some all-electric designs are circular, such as Pochet and SORG VSM designs.) However, there are significant dead (low flow or stagnant) regions that result from the rectangular construction.
Submerged combustion has been proposed in several patents for application in commercial glass melting, including U.S. Pat. Nos. 4,539,034; 3,170,781; 3,237,929; 3,260,587; 3,606,825; 3,627,504; 3,738,792; 3,764,287; 6,460,376; 6,739,152; 6,857,999; 6,883,349; 7,273,583; 7,428,827; 7,448,231; and 7,565,819; and published U.S. Patent Application Nos. 2004/0168474; 2004/0224833; 2007/0212546; 2006/0000239; 2002/0162358; 2009/0042709; 2008/0256981; 2007/0122332; 2004/0168474; 2004/0224833; and 2007/0212546. In submerged combustion glass melting, the combustion gases are injected beneath the surface of the molten glass and rise upward through the melt. The glass is heated at a higher efficiency via the intimate contact with the combustion gases. However, using submerged combustion burners does not alleviate dead flow regions that result from the rectangular construction of the melter itself.
Energy costs continue to increase, spurring efforts to find ways to reduce the amount of fuel in glass manufacturing. Oxy-fuel burners have been used in the glass industry in general, especially in the fiberglass, TV glass, and container glass industry segments. There are few complete oxy-fuel fired float furnaces in operation today and they have been using retrofit oxy-fuel burners designed specifically for smaller container or fiberglass furnaces. These conversions were most likely made to meet emissions standards. Known oxy-fuel burners are predominately nozzle mix designs and avoid premixing for safety reasons due to the increased reactivity of using oxygen as the oxidant versus air. Some common designs of nozzle mix oxy-fuel burners are described in U.S. Pat. Nos. 5,199,866; 5,490,775; and 5,449,286. The concept of nozzle mix oxy-fuel burners is to mix fuel and oxygen at the burner nozzle. The flame produced is a diffusion flame with the flame characteristics determined by mixing rates. Short intense flames are most common with these burners, however some delayed mixing geometry are considered to generate longer luminous flames. More recently, “flat flame” burners have been used in the industry for melting applications, in which the flame is above the melt and generally parallel thereto. These burners produce a flame that is 2 to 3 times wider than a traditional (cylindrical) oxy-fuel flame. U.S. Pat. Nos. 5,545,031; 5,360,171; 5,299,929; and 5,575,637 show examples of flat flame burners. The above-mentioned U.S. Pat. No. 7,273,583 describes a submerged combustion burner having co-axial fuel and oxidant tubes forming an annular space therebetween, wherein the outer tube extends beyond the end of the inner tube. A burner nozzle having an outside diameter corresponding to the inside diameter of the outer tube is connected to the outlet end of the inner tube and forms a centralized opening in fluid communication with the inner tube and at least one peripheral longitudinally oriented opening in fluid communication with the annular space. A longitudinally adjustable rod may be disposed within the inner tube for adjustment of fluid flow therethrough, and a cylindrical insert having a flame stabilizer for stabilizing a flame produced by the burner is attached to the outlet end of the outer tube. All of the patent documents referenced in this document are incorporated herein by reference.
It would be an advance in the glass melting art to develop non-rectangular melting furnaces (“melters”) that have reduced dead flow (stagnant) regions, while taking advantage of the efficiency of submerged combustion burners, to increase melter throughput and produce high quality molten glass.